The antiquity of water supply systems is well established. The practice of water treatment dates back to at least 2000 B.C., when Sanskrit writings on medical lore recommended storage of water in copper vessels, exposure of water to sunlight, filtering through charcoal, and boiling of foul water for the purpose of making water drinkable.
Later, two significant advancements helped to establish drinking water treatment. In 1685, the Italian physician Lu Antonio Porzio designed the first multiple-stage filter. Prior to that, in 1680, the microscope was developed by Anton Van Leeuwenhoek. With the discovery of the microscope enabling the detection of microorganisms and the ability to filter out these microorganisms, the first water-filtering facility was built in the town of Paisley, Scotland, in 1804 by John Gibb. Within three years, filtered water was piped directly to customers in Glasgow, Scotland.
In 1806, a large water treatment plant began operating in Paris with filters made of sand and charcoal, which had to be renewed every six hours. Pumps were driven by horses working in three shifts. Water was then settled for twelve hours before filtration.
In the 1870's, Dr. Robert Koch and Dr. Joseph Lister demonstrated that microorganisms existing in water supplies can cause disease, and then began the quest for effective ways to treat raw water. In 1906, in eastern France, ozone was first used as a disinfectant. A few years later, in the United States, the Jersey City waterworks in 1908 became the first utility in America to use sodium hypochlorite for disinfecting the water supply. Also, in that same year, the Bubbly Creek Plant in Chicago, Ill., instituted chlorine disinfectant. Over the next several decades, work began on improving the efficiency of filtration and disinfectant.
By the 1920's, the filtration technology had evolved so that pure, clean, bacteria free, sediment free, and particulate free water was available. During World War II, Allied military forces operated in arid areas and began ocean water desalination in order to supply troops with fresh drinking water. In 1942, the U.S. Public Health Service adopted the first set of drinking water standards, and the membrane filter process for bacteriological analysis was approved in 1957.
By the early 1960's, more than 19,000 municipal water systems were in operation throughout the United States. With the 1974 enactment of the Safe Drinking Water Act, the federal government, the public health community and water utilities worked together to provide secure water production for the United States.
The world has a shortage of potable water for drinking and water for agricultural, irrigation, and industrial use. In some parts of the world, prolonged drought and chronic water shortages have slowed economic growth and may eventually cause the abandonment of certain population centers. In other parts of the world, an abundance of fresh water exists, but the water is contaminated with pollution such as chemicals from industrial sources and from agricultural practices.
The world faces severe challenges in our ability to meet our future water needs. Today there are over 300 million people living in areas with severe water shortages. That number is expected to increase to 3 billion by 2025. About 9,500 children die around the world each day because of poor quality drinking water according to United Nations reports. The population growth has increased the demand on drinking water supplies, while the available water, world wide, has not changed. In the coming decades, in addition to improving water reuse efficiency and promoting water conservation, we will need to make additional water resources at a cost and in a manner that supports urban, rural and agricultural prosperity and environmental protection.
There has been a 300 percent increase in water use over the past 50 years. Every continent is experiencing falling water tables, particularly on the southern Great Plains and the Southwest in the United States, and in North Africa, Southern Europe, the entire Middle East, Southeastern Asia, China and elsewhere.
Evaporation and reverse osmosis are two common methods to produce potable water from sea water or brackish water. Evaporation methods involve heating sea water or brackish water, condensing the water vapor produced, and isolating the distillate. Reverse osmosis is a membrane process in which solutions are desalted or purified using relatively high hydraulic pressure as the driving force. The salt ions or other contaminants are excluded or rejected by the reverse osmosis membrane while pure water is forced through the membrane. Reverse osmosis can remove approximately 95% to approximately 99% of the dissolved salts, silica, colloids, biological materials, pollution, and other contaminants in water.
The only inexhaustible supply of water is the sea. The desalination of sea water using a land-based plant in quantities large enough to supply a major population center or large scale irrigation projects presents many problems. Land-based plants that desalinate sea water through evaporation methods consume enormous amounts of energy.
Land-based plants that desalinate water through reverse osmosis methods generate enormous quantities of effluent comprising the dissolved solids removed from the sea water. This effluent, also referred to as concentrate, has such a high concentration of salts, such as sodium chloride, sodium bromide, etc., and other dissolved solids that simply discharging the concentrate into the waters surrounding a land-based desalination plant would eventually kill the surrounding marine life and damage the ecosystem. In addition, the concentrate that emerges from conventional land based reverse osmosis desalination plants has a density greater than sea water, and hence, the concentrate sinks and does not quickly mix when conventionally discharged directly into the water surrounding a land-based plant.
Even if the health of the marine life and ecosystem surrounding a land-based reverse osmosis desalination plant was not a concern, discharging the concentrate into the water surrounding the land-based plant would eventually raise the salinity of the intake water for the plant and foul the membranes of the reverse osmosis system. If a membrane in a reverse osmosis system is heavily fouled, it must be removed and treated to eliminate the fouling material. In extreme cases, the fouling material cannot be removed, and the membrane is discarded.
As a result of all of these factors, potable water produced from land-based reverse osmosis desalination plants is costly and presents significant engineering problems for disposing of the effluent. Hence, despite the world's shortage of potable water, only a small percentage of the world's water is produced by the desalination or purification of water using reverse osmosis methods. Therefore, the need exists for a method and system to consistently and reliably supply potable water using desalination technology that does not present the engineering and environmental problems that a conventional land-based desalination plant presents.
Known ship-board water desalination systems are designed and operated for ship-board consumption of water, and thus are designed and operated according to various maritime standards. Maritime standards for water desalination systems and plants and water quality are less stringent than the standards governing the design and operation of land-based desalination plants and systems, especially those promulgated by the United States, United Nations, and World Health Organization. With the world's increasing shortage of potable water, a need exists to alleviate this shortage. Therefore, there is a demonstrable need for methods and systems that can be utilized at sea to provide desalinated water for land-based consumption. Moreover, the desalinated water produced at sea can be stored, maintained, and transported in a manner consistent with those regulations and standards governing the design and operation of land-based water desalination plants and systems.